In the travels of the New Frontiers in the novel, the colonists run across a very tidy little planet inhabited by The Little People.

One thing he did learn, and its implications opened up whole new fields of thought: the Little People had, in one sense, conquered death.

Since each of their egos was shared among many bodies, the death of one body involved no death for the ego. All memory experiences of that body remained intact, the personality associated with it was not lost, and the physical loss could be made up by letting a young native "marry" into the group. But a group ego, one of the personalities which spoke to the Earthmen, could not die, save possibly by the destruotion of every body it lived in. They simply went on, apparently forever.

Their young, up to the time of "marriage" or group assimilation, seemed to have little personality and only rudimentary or possibly instinctive mental processes. Their elders expected no more of them in the way of intelligent behavior than a human expects of a child still in the womb. There were always many such uncompleted persons attached to any ego group; they were cared for like dearly beloved pets
or helpless babies, although they were often as large and as apparently mature to Earth eyes as were their elders.

In the novel, it is also possible for people to join these groups. One of the Howard Families, Mary Sperling, does so:

Mary Sperling, moved by conviction of her own impending death, saw in the deathless group egos a way out. Faced with the eternal problem of life and death, she had escaped the problem by choosing neither . . . selflessness. She had found a group willing to receive her, she had crossed over.

The idea of a group mind can be found as early as 1930 in Olaf Stapledon's Last and First Men.